Col live in luxury on the Upper Decks of the juggernaut Worldshaker, a mobile city as big as a mountain. Far Below, the Filthie toil amidst the grime, powering the massive engines. Col has been chosen as the next Supreme Commander – but then a girl Filthy escaped from Below and appears in his cabin. “Don’t let them take me!” she begs. Will he hand her over, or will he break all the rules? Col’s safe, elite world is about to fall apart.

Uled, the creator of the plantlike Aern, the carnivorous Vael, and the multitudinous varieties of the reptilian Zaur, has completed his plan to return from the dead, creating the possibility of "undeath" in the process. Prince Rivvek has achieved peace between his people and the Aern, but at the cost of his capital city and the departure of a large portion of his military on a suicide mission to attempt the rescue of the Lost Command (a group of one thousand Armored Aern, who carried their assault in the Never Dark as a gambit to help win the last Demon War). The goal is to gain the forgiveness of the Aern and to be accepted as something other than Oathbreakers by Rae'en, the leader of the Aern and daughter of Kholster. Kholster, having replaced Torgrimm as the god of death, must work together with other new deities to determine the extent of Uled's plans. He intends to stop them from going any further and somehow bring balance to the heavens while preventing holy wars...